The carbohydrate binding site of concanavalin A (con A) has been investigated by measuring the distance between Mn2 ion and the fluorine atoms in N-trifluoroacetylated glucosamine. In both con A dimers and tetramers, the sugar binds at the same distance from the transition metal atom. The kinetics of Mn 2 ion association with demetallized con A has been examined by using the electron spin resonance signal of the Mn2 ion. Rates of binding of Mn2 ion show a pH optimum around pH 6.0 with residues having pK's 0.5 units above and below that being important in binding. The pH optimum varies slightly with Ca2 ion concentration. Binding of several substrates which are routinely used for determining con A binding activity has been examined as a function of pH and metal ion composition. Metal ion requirements are strict at or near pH 5.0 but are less stringent near pH 7.0. The kinetics of Mn2 ion dissociation are also being investigated in order to correlate the dissociation reaction with the association steps. Both water proton relaxation measurements and Cl35 nuclear resonances are being used to monitor different states in the association and dissociation process.